Control of Pythium Blight of Snap Beans by Seed Treatment with Systemic Fungicides

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Abstract
The systemic fungicide metalaxyl applied to snap bean (P. vulgaris) seed directly or with acetone infusion significantly reduced blight in the greenhouse and field in soils naturally infested with Pythium ultimum, P. aphanidermatum and P. myriotylum. Directly applying as little as 0.2 g a.i.[active ingredient]/kg of seed using either a 50WP or 2E formulation controlled preemergence damping-off and postemergence blight without phytotoxicity. Efficacy of metalaxyl against blight was reduced during incubation at a high temperature (35.degree. C). Metalaxyl and propamocarb hydrochloride seed treatments generally gave better protection than ethazol against Pythium blight. In liquid culture, metalaxyl had an ED50 of < 1 .mu.g a.i./ml in inhibiting mycelial growth of the 3 Pythium spp., with P. ultimum the most sensitive. Zoospore and oospore germination and sporangial formation were less sensitive to metalaxyl than mycelial growth. Metalaxyl did not affect membrane permeability at 50 .mu.g/ml, and cholesterol had no effect on leakage.

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